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在上一篇文章里叙述了利用西西伯亚沙依姆油田罗文采油场的垂直地震剖面资料使用纵波型首波构制速度的剖面二篇文章则介绍用其横波型首波构造制该地区速度剖面的方法及研究结果。 相似文献
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本文分析了简化模型下声波测井时裸眼井（内充流体一般是泥浆）中弹性波的传播,此波场可看成是轴向传播有不同波矢的分波的叠加。分析表明,对于井外只有单一均匀岩层且无限深的井,仅对如（18）式所示的特征频率成分才存在具有轴向传播最大相速度vzm=c2的所谓“首波”;而vx > c2及c2 > vz>b2的分波却不存在,此处c2和b2分别是井外岩层的纵波和横波速度。这正解释了文献[3]中所报道的裸眼井的“过滤效应”。分析还表明,对于井外具有多层岩层的井,只在一定条件下才存在与上述特性相近的“首波”。本文结果对声速测井显然是重要的。 相似文献
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利用全波场和分波场算法对裸眼井软地层中由单极子源和多极子源（偶极子源和四极子源）激发的弹性波进行了数值研究,给出了声波全波列理论波形、纯纵波和纯横渡理论波形及纵横波的频率传输特性曲线.结果表明,纯纵波和纯横波是无频散几何衰减波;除了在vs>（1-ρ1/ρ2）1/2v1的井眼中由单极子源激发的横波无传播特征频率外,纵横波都具有各自的传播特征频率,纵波的传播特征频率有一系列离散值,横波的传播特征频率只有一个且等于非对称模式波的截止频率;多极子源激发的纵波传播特征频率的最小值大于横波的传播特征频率,随着极子数增多,二者的特征频率值皆增高,差别也越大,因此,当声源发射主频较低,接近横波传播特征频率而远离纵波传播特征频率时,低频多极子源将压制纵波并激发出较强的横波,分析结果还表明,通常所说的低频多极子源激发出的横波波群实际上是纯横波与截止频率附近的非对称模式波叠加的结果,在其它条件不变时,二老对横波波群相对贡献的大小取决于声源激发主频的高低及其带宽的大小. 相似文献
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钻井中首波的共振与衰减 总被引：6，自引：2，他引：4
本文从P波首波的严格割线积分出发,首次给出了揭示其共振与衰减特性的渐近展开式,通过数值计算,对这些公式进行了检验,证明它们与严格解符合的相当好.解析的和数值结果一致表明:首波具有共振特性,频谱是连续的;振幅随源距z按1/z规律衰减;各共振峰幅度随岩石泊松比v的增大按[v/（1-v）]2规律增大.时域计算表明,所谓“滤波效应”正是首波共振激发特性的反映,传播过程中不频散. 相似文献
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利用合成理论地震图方法研究了存在高速层或低速层的地壳模型及壳-幔过渡带模型中首波等震相的动力学特征，指出首波的特征对于高速层的结构变化比较敏感．当高速层厚度与特征波长相比较小时，地震波的衍射现象明显，这种情况下高速层不能屏蔽在其下面一层的上界面传播的首波，且该首波震相的强度随高速层厚度或速度的增加而递减；当高速层厚度与特征波长相当时，高速层底面的反射波震相与首波震相到时接近，会因互相干涉而减弱；对于低速层，首波震相强度较弱且随低速层速度的减小而递减；在壳-幔间断处引入一定厚度和速度变化范围的过渡带，可以得到更加明显的视首波震相，强度随过渡带厚度或速度变化范围的增加而增大． 相似文献
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利用井孔首波求取Vs和Qp值的广义线性反演方法的应用研究 总被引：2，自引：2，他引：2
针对声全波幅度信息的利用还非常有限的实际情况，本文以更加接近实际的柱状声源在各向同性准弹性介质包围的轴对称井孔中激发的波场理论为基础，建立了利用首波幅度来以地层横波速度Ｖｓ和介质纵波品质因素Ｑｐ的广义线性反演模型，首先，通过数值计算是到该方法在长源距声全波测井的测量频率范围内，对地层介质泊松比σ约小于０．３６的情况下适用。 相似文献
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对断裂带及附近区域地层精细结构的描述是理解地震孕育和发生过程的基础.不同板块或块体边界在构造或区域应力作用下,常常会形成速度间断面和低速的断裂带,间断面和低速带的存在会产生特殊的断裂带地震波,比如断裂带首波和围陷波,并会影响地震的物理过程、破裂速度和破裂方向等.本文主要利用2010年4月14日M_W6.9玉树地震后布设的流动地震台站,对沿着甘孜—玉树断裂带传播的断裂带首波进行识别和分析.分析结果表明,在甘孜—玉树断裂带的不同区域均观测到了断裂带首波,在西段的结隆拉张盆地附近的3个台站沿断裂带界面的平均纵波速度差异值在5%～8%,而其他区域的平均速度差异为1%～3%.通过台站位置分布和断裂带首波特征关系,初步分析了断裂带拉张盆地的结构,结果显示结隆盆地的长度为～40km,宽度为5.35～5.97km,深度不超过5km,在地表浅层形成了一个低速区,分别与巴颜喀拉块体(NE)和羌塘块体(SW)产生了两个物性差异界面,但没有延伸到主震和余震区震源深度.我们的结果表明结合密集台阵资料,通过断裂带首波特征分析可以为断裂带精细结构及几何特征提供一种新的技术方法和途径. 相似文献
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通常首波被认为是以下层高速度沿着平坦界面传播的折射波。然而,沿着不规则界面首波的传播路径至今仍不明确。在这里,我们将利用重叠单元(SEMO)方法以模拟的方式来研究这个问题。之所以选择重叠单元方法,是因为这种方法可以准确地计算出沿不规则界面传播的界面波。然后我们利用时间窗将首播从界面波中分离出来,并分析首播沿不规则界面传播进程中能量的变化和走时的变化。分析结果表明,与平坦的界面上首播的传播情况不同,沿不规则界面传播的首播由两种机制产生:折射机制和透射机制,也就是说,首播可能是沿界面传播的折射波或高速介质中向低速介质的透射波。关于首播的这种认识将有助于我们建设更加精确的首播反演方法,例如建立更为精确的首波旅行时层析成像,并由此获得更准确的地下结构模型,这对于研究认识一些特殊地区(如青藏高原)的形成机制是非常重要的。 相似文献
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在上一篇文章里叙述了利用西西伯利亚沙依姆油田罗文采油场的垂直地震剖面资料使用纵波型首波构制速度剖面的方法。本篇文章则介绍用其横波型首波构制该地区速度剖面的方法及研究结果。 相似文献
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Dispersion and radial depth of investigation of borehole modes 总被引：2，自引：0，他引：2
Sonic techniques in geophysical prospecting involve elastic wave velocity measurements that are performed by placing acoustic transmitters and receivers in a fluid‐filled borehole. The signals recorded at the receivers are processed to obtain compressional‐ and shear‐wave velocities in the surrounding formation. These velocities are generally used in seismic surveys for the time‐to‐depth conversion and other formation parameters, such as porosity and lithology. Depending upon the type of transmitter used (e.g. monopole or dipole) and as a result of eccentering, it is possible to excite axisymmetric (n= 0) , flexural (n= 1) and quadrupole (n= 2) families of modes propagating along the borehole. We present a study of various propagating and leaky modes that includes their dispersion and attenuation characteristics caused by radiation into the surrounding formation. A knowledge of propagation characteristics of borehole modes helps in a proper selection of transmitter bandwidth for suppressing unwanted modes that create problems in the inversion for the compressional‐ and shear‐wave velocities from the dispersive arrivals. It also helps in the design of a transmitter for a preferential excitation of a given mode in order to reduce interference with drill‐collar or drilling noise for sonic measurements‐while‐drilling. Computational results for the axisymmetric family of modes in a fast formation with a shear‐wave velocity of 2032 m/s show the existence of Stoneley, pseudo‐Rayleigh and anharmonic cut‐off modes. In a slow formation with a shear‐wave velocity of 508 m/s, we find the existence of the Stoneley mode and the first leaky compressional mode which cuts in at approximately the same normalized frequency ωa/VS= 2.5 (a is the borehole radius) as that of the fast formation. The corresponding modes among the flexural family include the lowest‐order flexural and anharmonic cut‐off modes. For both the fast and slow formations, the first anharmonic mode cuts in at a normalized frequency ωa/VS= 1.5 approximately. Cut‐off frequencies of anharmonic modes are inversely proportional to the borehole radius in the absence of any tool. The borehole quadrupole mode can also be used for estimating formation shear slownesses. The radial depth of investigation with a quadrupole mode is marginally less than that of a flexural mode because of its higher frequency of excitation. 相似文献
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This paper describes the three phenomena observed in full wave experiments： 1. the amplitudes （absolute value） of the first compressional and shear arrivals have the same variation rules; 2. the phases of the first compressional and shear arrivals are always opposite to each other; and 3. the amplitude variation periods of the first compressional and shear arrivals are 2π. A full analysis and interpretation points out that these phenomena should appear under the full wave logging condition. Hence,the basis of using phase diffrences to extract useful information from the full wave is found. 相似文献
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CLAUDIA KERNER 《Geophysical Prospecting》1990,38(2):111-137
Alekseev and Mikhailenko have developed a wavenumber-summation method which combines a finite integral transformation with a finite-difference calculation and involves no approximations other than numerical ones. However, numerical anisotropy causes velocity errors for shear waves which are unacceptable if Poisson's ratios are larger than 0.4 and unless the number of grid points per wavelength is chosen considerably higher than the value generally regarded as sufficient in finite-difference computations. To overcome this limitation in the applicability of the otherwise very powerful modelling scheme, the method is applied to the elastodynamic equations for the velocity vector. Thus, instead of solving a second-order hyperbolic system as in the case of the wave equation, solutions to a first-order hyperbolic system are computed. The finite-difference iteration is performed in a staggered grid. In addition to mastering the numerical difficulties in cases where the Poisson's ratio is unusually high, this approach results in a code which can be used for the modelling of liquid layers. With the new scheme, water reverberations are investigated in terms of normal modes. It is found that for realistic sea-bottom velocities the critical and supercritical cases exist only for P-waves. It means that compressional waves are trapped within the water layer but energy leaks into the substratum through converted shear waves. These leaky compressional normal modes attain properties similar to those of shear normal modes or Pseudo-Love waves. Due to their origin from conversion of dispersed multi-modal compressional waves the shear waves generated at the sea-bottom form a long complex wavetrain. They were found to mask the reflections from the target horizon in an offset-VSP field section. 相似文献
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声波测井中的纵波和横波 总被引：2，自引：0，他引：2
充流体井中声传播理论是声波测井的理论基础。Blot（1952）绘出了充流体井中简正模式和斯通利波的频散曲线,White等（1968）首先计算了合成全波列波形,Peterson（1974）和余寿绵（1984）导出了简正模式和斯通利波的振幅表达式。余寿绵还预言纵波和横波是一种共振现象,为沿轴向传播存在特征频率的不衰减波。但是,现行理论认为纵 相似文献
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本文从数值上研究了裸眼井中弹性波传播的非对称模式,给出了合成微地震图和导波（弯曲波）的频散曲线,发现在“硬”地层和“软”地层的井中,导波都是高度频散的,其最大相速度等于地层的横波速度,其截止频率低于对称模式的伪瑞利波的截止频率;在低频（2-3kHz）和长源距（3-4m）的条件下,由非对称的声源（如声偶极子）所产生的微地震图中,初至信号是以横波速度传播的,而以纵波速度传播的信号被抑制。本文的结果对研制横波速度测井仪是有意义的。 相似文献
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Free vibration of soils happens frequently during some large earthquakes, perhaps seeming like a paradox. This happens because the energy released from seismic sources in some cases is not stationary in time, allowing relaxation intervals in between without important seismic wave arrivals in which free soil vibration happens. Two techniques to estimate the natural period of the free vibration from accelerograms are presented: autocorrelograms and Fourier spectra. Both techniques sometimes allow measuring higher mode frequencies of the soil for the three first modes as well as modal damping. Free vibration modal periods satisfy the classic 1D equation S-wave theory. The presence of free vibrations corresponds to shear wave soil energy radiation episodes rather than to energy amplification of incoming stationary seismic shear waves suggested by the dynamic soil amplification. These results explain the discrepancies observed between the theoretical soil dynamic amplification and the accelerographic measurement. Observation of free vibration of soils is not always possible, it depends on the duration of the time windows without important seismic waves arrivals compared to the natural period and damping of the soil. 相似文献
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Compressional-wave Q estimation from full-waveform sonic data 总被引：1，自引：0，他引：1
There is significant evidence that the anelastic loss of seismic energy is linked to petrophysical properties such as porosity, permeability and clay content. Thus, reliable estimation of anelastic attenuation from seismic data can lead to improved methods for the prediction of petrophysical properties. This paper is concerned with methods for the estimation of attenuation at sonic frequencies (5–30 KHz) from in situ data. Two independent methods have been developed and tested for estimating compressional‐wave attenuation from full‐waveform sonic data. A well‐established technique, the logarithm spectral ratio (LSR) method, is compared with a new technique, the instantaneous frequency (IF) method. The LSR method uses the whole spectrum of the seismic pulse whilst the IF method uses a carefully estimated value of instantaneous frequency which is representative of the centre frequency of the pulse. In the former case, attenuation estimation is based on the relative variation of amplitudes at different frequencies, whilst in the latter case it is based on the shift of the centre frequency of the pulse to lower values during anelastic wave propagation. The IF method does not assume frequency independence of Q which is a necessary assumption for the LSR method, and it provides a stable frequency log, the peak instantaneous frequency (PIF) log, which may be used as an indicator for attenuation under certain limitations. The development and implementation of the two methods is aimed at minimizing the effect of secondary arrivals, such as leaky modes, and involved a series of parameter tests. Testing of the two methods using full‐waveform sonic data of variable quality, obtained from a gas‐bearing sandstone reservoir, showed that the IF method is in general more stable and suitable for full‐waveform sonic data compared with the LSR method. This was evident especially in data sets with high background noise levels and wave‐interference effects. For good quality data, the two methods gave results that showed good agreement, whilst comparison with other log types further increased confidence in the results obtained. A significant decrease (approximately 5 KHz) in the PIF values was observed in the transition from an evaporite/shale sequence to the gas‐bearing sandstone. Average Q values of 54 and 51 were obtained using good quality data from a test region within the gas‐saturated sandstone reservoir, using the LSR and IF methods, respectively. 相似文献